An industry group is blasting a new report that accuses Eversource and Avangrid of artificially constraining New England natural gas pipeline capacity, leading to $3.6 billion in financial gain between 2013 and 2016.

The claim "is false and, frankly, ridiculous," said the Northeast Gas Association in a statement, adding that the Environmental Defense Fund white paper is "profoundly misleading and inaccurate."

The report claims that "down-scheduling" -- where gas utilities reserve day-ahead capacity and then don't use it -- increased natural gas and electricity prices by an average of 38 and 20 percent, respectively, within the three-year period.

The gas association said power plants see no change in profit when the price of natural gas rises or falls, because the cost of energy is treated as a pass-through expense.

"The allegations made regarding Avangrid and Eversource are reckless and unwarranted," the statement reads.

Avangrid and Eversource last week condemned the study. They said they did nothing wrong, had the full approval of regulators, and acted prudently to ensure they could serve their home heating and business customers, which are guaranteed fuel via long-term "firm transportation" contracts.

After those customers are served, excess capacity may be purchased by power plants on the spot market. During the 2013-14 "polar vortex," which brought frigid temperatures to the Northeast for much of the winter, energy prices spiked because of market scarcity. Since then, market reforms have lessened price volatility.

Berkshire Gas, with its 40,000 accounts in Western Massachusetts, is a subsidiary of Avangrid, which also owns gas utilities in Connecticut, Maine and New York. Eversource owns Yankee Gas in Connecticut and NSTAR Gas in Massachusetts. Both companies also own electrical utilities and power generation assets.

Eversource also owns fossil fuel and hydroelectric power plants in New Hampshire, but is in the process of selling them. New Hampshire was the final state in New England to rule that regulated utilities may not own power plants.

Media representatives for the Environmental Defense Fund did not respond to telephone messages and an email from The Republican seeking comment.

Eversource, the former Northeast Utilities, was formed in 2015. Its utility subsidiaries -- Connecticut Light and Power Co., NSTAR Electric, NSTAR Gas, Public Service Co. of New Hampshire, Western Massachusetts Electric Co. and Yankee Gas -- included 3.6 million customers in Connecticut, Massachusetts and New Hampshire.

Avangrid has gas and electric utilities in New England and New York, and was formed in 2015 in a $3 billion merger. In Western Massachusetts, Berkshire Gas is owned by Avangrid.

As for allegations that the two firms reserved too much pipeline capacity on cold days, then didn't use it, the association said "it is common sense to err on the side of caution" to have a safety margin to cover unexpected operational issues.

"That is what Avangrid and Eversource did," the statement read. "We can only imagine the outcry if they had failed to reserve enough gas supply and homeowners, schools, hospitals, nursing homes, businesses, and industry lost access to fuel.